Optical materials are much studied these days, and especially in the field of lenses, it is strongly desired to develop materials having high refraction properties, heat resistance, transparency, easy moldability, lightweight properties, chemical resistance and solvent resistance.
As compared with inorganic materials such as glass, plastic lenses are lightweight and are hardly cracked, and they can be worked into various shapes. Accordingly, these days, they are being much popularized not only for eyeglass lenses but also for other various optical materials such as lenses for portable cameras and pickup lenses.
With that, the plastic material itself for lenses is desired to have high refractive index for obtaining thin lenses and downsized pickup devices. For example, a technique of introducing a sulfur atom into a polymer (see JP-A-2002-131502 and JP-A-10-298287), and a technique of introducing a halogen atom and an aromatic ring into a polymer (see JP-A-2004-244444) are being much studied. However, a plastic material having high refractive index and having good transparency so as to be substitute for glass is not as yet developed. Further, in optical fibers and optical waveguides, materials having different refractive indexes are used in combination, or a material having distributed refractive index is used. Thus, to provide a material having different refractive index by sites, development of a technique that can optionally control a refractive index is desired.
From that it is difficult to increase a refractive index with only an organic material, a technique of increasing a refractive index of a resin by dispersing an inorganic material having high refractive index in a resin matrix is reported (see JP-A-2003-73559). To reduce transmitted light attenuation due to Rayleigh scattering, it is preferable to uniformly disperse inorganic fine particles having a particle size of 15 nm or less in a resin matrix. However, primary particles having a particle size of 15 nm or less are very liable to agglomerate, and therefore, it is extremely difficult to uniformly disperse those in a rein matrix. Further, considering transmitted light attenuation in optical path length corresponding to a thickness of a lens, the amount of inorganic fine particles added must be limited. For this reason, it has not hitherto been realized to disperse fine particles in a resin matrix in high concentration without deteriorating transparency of a resin.
A resin composition molding which is a molding mainly comprising a thermoplastic resin composition having dispersed therein ultrafine particles having a number average particle size of from 0.5 to 50 nm and has a birefringence per 1 mm optical path length of 10 nm or less on the average (see JP-A-2003-147090), or a thermoplastic material resin composition comprising a thermoplastic resin having a refractive index shown by a specific equation and Abbe number and inorganic fine particle having specific average particle diameter and refractive index, and an optical component using the composition are reported (see JP-A-2003-73563 and JP-A-2003-73564). Those are that inorganic fine particles are dispersed in a resin, but any of those did not exhibit sufficient performances from the standpoint that fine particles are dispersed in a resin matrix in high concentration without deteriorating transparency of a resin.
On the other hand, for an organic-inorganic hybrid composition, a method of melt kneading surface organic-modified inorganic particles and an acidic group-containing resin is reported, but the amount of the inorganic particles added is about 1% by mass, and it is not said to be sufficient (see JP-A-2004-217714). Further, an organic-inorganic hybrid composition in which a surface-modifying group of inorganic particles and a resin are bonded through a linker is reported (see JP-T-2004-352975 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application)). However, operation is complicated such that high temperature is required for bond formation, and there is the possibility of gelation. Thus, the composition did not exhibit sufficient performance from the standpoint of processability. Further, there is no any disclosure in any of those Patent Documents regarding a thick transparent article that can be used in lenses having high refractive index.